Cooling of electronic displays

ABSTRACT

An electronic display has a housing with different regions and a display panel with a display surface. A cooling module flows internal coolant through the cooling module and the regions. The cooling module has a crossflow heat-exchanger and side walls. The regions and cooling module have an coolant inlet and outlet. The coolant inlets of the regions communicate with the coolant outlet of the cooling module. The coolant outlets of the regions communicate with the coolant inlet of the cooling module. The regions have their own circulating loop of coolant, with flow of coolant being deflected from the outlet of the cooling module towards the coolant inlets of the regions, and flow of coolant from the coolant outlets of the regions being deflected towards the coolant inlet of the cooling module. The coolant flows in parallel over both front and back of the display panel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Stage application of International ApplicationNo. PCT/GB2018/051151, filed Apr. 30, 2018, which claims the benefit ofpriority to GB Application No. 170768.7, filed Apr. 28, 2017. The entirecontents of these prior applications are incorporated by referenceherein.

FIELD

The present invention relates to cooling of electronic displays It isconcerned particularly, although not exclusively, with large-scaleelectronic displays that incorporate crossflow heat-exchangers. In thecontext of this specification, “large-scale” means a minimum visiblescreen size of approximately 50 inches (127 cm), measured diagonallyacross the screen.

BACKGROUND

Electronic advertising displays are being used increasingly. They areused in outdoor as well as indoor venues; in locations such astraditional roadside and city centre billboard locations, travelenvironments (e.g. rail platforms, airports, bus stops, trams,underground rail), retail environments (e.g. shopping malls,supermarkets, petrol stations), entertainment venues (e.g. stadiums,arenas, cinemas, restaurants, bars) and typically any location whereadvertisers can reach large audiences as they go about their day to daybusiness.

Such displays typically use LCD or LED technology and are designed tocater for outdoor environmental conditions such as weather, temperature,water, wind loading, etc and are designed to withstand robustenvironments e.g. vandalism and accidental impacts e.g. from vehicles,shopping trolleys, people, etc.

Such displays are typically large—e.g. high brightness 70 inches (178cm) or more visible screens that can be viewed by a mass audience from adistance and require varied fixing mechanisms to suit the variedapplication needs—e.g. ground fixed (with suitable foundations), wallmounted, integrated with structures e.g. bus-stops—and often with somecreative or branded design to suit the marketing needs of brand,retailer or display owner.

Such displays are typically heavy, incorporating a substantial chassiswith high thermal mass. Changes in ambient conditions, such astemperature and humidity, can lead to unwanted condensation that can bea danger to electronics within the display. This can be a particularproblem when the display is started up after being idle overnight, whenthe ambient temperature may have dropped considerably. Whilst displaysoften incorporate a heat-exchanger as part of a cooling system, toprevent the display from overheating in warm or sunny conditions, theheat-exchanger may contribute to condensation problems upon start-up ofthe display, or due to unfavourable ambient conditions whilst thedisplay is running. It is common for heat-exchangers to have cold spots,where condensation may tend to form.

BRIEF SUMMARY

Preferred embodiments of the present invention aim to provide electronicdisplays with improved cooling within the display, providingadaptability to differing configurations.

In the context of this specification, the term ‘heat-exchanger’ means adevice or an arrangement of components that provides heat exchangebetween two fluids, whilst preventing direct contact between the fluids.A heat-exchanger may be a dedicated device. Alternatively, heat exchangefunctionality may be provided by an arrangement of components in anapparatus—for example, an electronic display. In an electronic display,heat-exchange function may be provided in different areas—for example,adjacent the front or back of one or more display panel, adjacent anelectronic control assembly, and so on. Such heat-exchange functions maybe provided as parts of a common heat-exchanger or as individualheat-exchangers.

According to the present invention, there is provided an electronicdisplay comprising:

a housing that is divided internally into regions;

a display panel within one of said regions and having a display surfacethat is visible through the housing; and

a cooling module disposed within the housing and arranged to provide aflow of internal coolant through the cooling module and said regions,the cooling module having a crossflow heat-exchanger within the coolingmodule and side walls that define a path of flow of the internal coolantthrough the cooling module:

wherein each of said regions and said cooling module has a respectiveinternal coolant inlet and internal coolant outlet;

the internal coolant inlets of said regions communicate with theinternal coolant outlet of the cooling module and the internal coolantoutlets of said regions communicate with the internal coolant inlet ofthe cooling module;

the arrangement is such that, in use, each of said regions has its owncirculating loop of internal coolant, through the respective said regionand the cooling module, with flow of internal coolant being deflectedfrom the outlet of the cooling module towards the internal coolantinlets of said regions, and flow of internal coolant from the internalcoolant outlets of said regions being deflected towards the internalcoolant inlet of the cooling module; and

the internal coolant flows in parallel over both front and back of thedisplay panel, the display panel being spaced from the side walls of thecooling module.

The electronic display may comprise a plurality of display panels, eachin a respective one of said regions.

One of said regions may not have a display panel within it.

Said regions may comprise a front region and a back region of thehousing; and a display panel may be disposed in the front region withits display surface visible through a front face of the housing.

Preferably, the cooling module has side walls that extend between sidewalls of the housing.

Preferably, the side walls of the cooling module divide the housing intosaid regions.

Preferably, the internal coolant inlet and internal outlet of thecooling module face and are spaced from side walls of the housing.

Preferably, an internal coolant deflector faces the internal coolantoutlet of the cooling module and is operative to deflect internalcoolant from the cooling module into different circulating loops ofinternal coolant in different said regions.

Preferably, an internal coolant deflector faces the internal coolantinlet of the cooling module and is operative to deflect internal coolantfrom different circulating loops of internal coolant into the coolingmodule.

Preferably, said cooling module comprises a heat-exchanger and animpeller for providing a flow of internal coolant through the coolingmodule and said regions.

Preferably, said heat-exchanger has a path for external coolant that isintroduced into the heat-exchanger from externally of the housing andoutput from the heat-exchanger to externally of the housing, theexternal coolant exchanging heat with internal coolant within theheat-exchanger without direct contact between the external and internalcoolant.

Preferably, said external coolant is air.

The electronic display may further comprise an electronic controlassembly arranged to control functions of the display, the assemblybeing located in said cooling module downstream of the heat-exchanger sothat cooled internal coolant from the heat-exchanger passes over theassembly.

Preferably, said electronic control assembly comprises components withinan enclosure having an inlet and outlet for internal coolant and atleast one impeller arranged to provide flow of internal coolant throughsaid enclosure.

Preferably, said internal coolant is air.

Preferably, the display is a large-scale electronic display.

Preferably, said display panel is an LCD panel.

Preferably, said display panel has an associated backlight.

An electronic display according to any of the preceding aspects of theinvention may comprise:

a housing;

a display panel within the housing and having a display surface that isvisible through the housing;

an electronic processor arranged to control functions of the display andoperating conditions within the housing;

input sensors disposed within the housing at distributed locations andarranged to sense operating conditions within the housing;

output components disposed within the housing at distributed locationsand arranged to respond to control signals; and

a bus connecting said input sensors, output components and electronicprocessor for intercommunication:

wherein processing of signals received from said input sensors andcontrol signals passed to the output components is distributed amongstmicrocontrollers that are local to said input sensors and outputcomponents and connect said input sensors and output components to saidbus.

Preferably, said operating conditions comprise environmental conditions.

Preferably, said input sensors comprise humidity sensors and temperaturesensors.

Preferably, said output components are operative to adjust environmentalconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example, to the accompanying diagrammatic drawings, in which:

FIG. 1 shows a crossflow heat-exchanger for use in a large-scaleelectronic display, with uniform air flow through the heat-exchanger;

FIG. 2A is a diagrammatic side view of a large-scale electronic displaywith a heat-exchanger and two LCD panels arranged back-to-back;

FIG. 2B is a diagrammatic front view of the display and heat-exchangerof FIG. 2A;

FIG. 2C is a diagrammatic front view of a heat-exchanger, internal fanarray and Electronics Control Assembly as juxtaposed within the displayof FIG. 2A;

FIG. 2D is a view similar to that of FIG. 2A but with a single LCDpanel;

FIG. 3 is a view similar to FIG. 1, illustrating a typicalheat-exchanger temperature characteristic;

FIG. 4 is a view similar to FIGS. 1 and 3, illustrating temperaturedifferentials at different points of the heat-exchanger;

FIG. 5 is a view similar to FIG. 4, but with external cooling airpassing through heat-exchanger channels at different flow rates;

FIG. 6 is a view similar to FIG. 5, with both external cooling air andinternal hot air passing through respective heat-exchanger channels atdifferent flow rates;

FIG. 7 illustrates sequences of operating states of a large-scaleelectronic display;

FIG. 8A is a flow chart illustrating a Cold Start process of thelarge-scale electronic display;

FIG. 8B is a flowchart similar to FIG. 8A, but employing a predeterminedpre-heat period;

FIG. 8C is a flowchart similar to FIG. 8B, but in which a heater iscontrolled as a device on a CAN bus;

FIG. 9 is a schematic diagram of elements and components for use in theCold Start process;

FIG. 10 is a flow chart illustrating a Warm Start process of thelarge-scale electronic display;

FIG. 11 is a schematic diagram of elements and components for use incontrolling dew point with a crossflow heat-exchanger of the large-scaleelectronic display;

FIG. 12 is a diagrammatic view of a heat-exchanger to illustrate areasat risk of generating internal condensation;

FIG. 13 is a flow chart illustrating a Normal Operation process of thelarge-scale electronic display; and

FIG. 14 is a flow chart illustrating a Powersave process of thelarge-scale electronic display.

DESCRIPTION OF EXAMPLE EMBODIMENTS

In the following description, for ease of reference, terms of positionand orientation are used conveniently to denote the position andorientation of items as shown in the figures. However, it will beappreciated that such items could be disposed in other positions ororientations, and terms such as “top”, “bottom”, “left”, “right”,“vertical”, “horizontal”, etc. are to be construed accordingly, toinclude such alternative positions and orientations.

It is to be understood that the various features that are described inthe following and/or illustrated in the drawings are preferred but notessential. Combinations of features described and/or illustrated are notconsidered to be the only possible combinations. Unless stated to thecontrary, individual features may be omitted, varied or combined indifferent combinations, where practical.

In the figures, like references denote like or corresponding parts.

In FIG. 1, a crossflow heat-exchanger 100 has first and second sets offluid-flow channels 103, 104 arranged such that each set crosses theother to afford heat-exchange between cooling air in the first set 103and hot air in the second set 104, without the cooling air and the hotair contacting one another. As shown in the figure, channels 103 may beseen as rows and channels 104 may be seen as columns. In this example,the channels 103, 104 cross each other substantially at right angles—butthey could cross at other angles.

In use, with reference to FIGS. 2A to 2C, the heat-exchanger 100 islocated within a closed housing 120 of a large-scale electronic displaythat generates heat, much of which is produced by a pair of LCD panels121 arranged in a back-to back configuration, such that the displaysurfaces of the LCD panels 121 face in opposite directions and arevisible through suitably transparent portions of the housing 120. Eachof the LCD panels 121 typically includes an LED backlight, whichgenerates heat. Sensitive electronics 122 and power supplies 123 arehoused within an Electronics Control Assembly (ECA) 134 located withinthe internal air path below the heat-exchanger 100. The sensitiveelectronics 122 may include a PC, router and sensors. External andinternal fan controllers 124, 125 are provided adjacent the externalairflow and internal airflow fans 101, 102 respectively.

Internal hot air flows through the columns 104 of the heat-exchanger 100from top to bottom, indicated by arrows I in FIG. 2B, whilst externalcooling air flows through the rows 103 of the heat-exchanger 100 fromright to left, indicated by arrows E in FIG. 2B.

The heat-exchanger 100 together with internal airflow fans 102 and ECA134 are located between a pair of baffles 126 that define an airflowpassage to direct internal airflow within the housing 120. The baffles126 extend the full width but not the full height of the housing 120, asshown by their upper edges 141 and lower edges 142 in FIG. 2B. Hotinternal air is drawn into the top of the heat-exchanger 100, as seen inFIG. 2A, and cooled internal air exits from the bottom of theheat-exchanger 100 to flow over the ECA 134. As it exits the bottom ofthe airflow passage between the baffles 126, the internal air isdeflected to back and front regions of the housing 120 by an inclined orcurved air deflector 143 and then flows upwardly over both front andback of the respective LCD panels 121. From the top of the LCD panels121, the heated internal air is deflected by the inner upper surface 144of the housing 120 and is then drawn back into the top of theheat-exchanger 100, where it repeats the loops just described. An airdeflector along the lines of air deflector 143 may be provided on theinner upper surface 144 of the housing 120.

As shown in FIG. 2C, the ECA 134 has its own housing 135 formed with oneor more input vent 132 (in this example, in a side face of housing 135,facing a baffle 126) and one or more output vent 133 (in this example,in the bottom of housing 135). One or more fan (e.g. 208, 317 in FIGS. 9and 11) located within the housing 135 draws cool internal air (from theheat-exchanger 100) into the ECA 134 and directs this air upward acrosssensitive electronics 122 within the ECA 134.

An internal baffle 131 within the ECA 134 guides internal cool air tothe top of the ECA and through a gap between the baffle 131 and the topof the housing 135. This air then passes downwards (propelled by the oneor more fan within the housing 135, each located adjacent a respectiveinput vent 132) over power supply assemblies 123 to provide cooling ofthe power supply assemblies. Air circulating within the ECA 134 isoutput at the one or more output vent 133 at the base of the housing135.

Cool internal air output from the heat-exchanger 100 (propelled byinternal air circulating fans 102) therefore passes over the outside ofthe ECA 134 and also passes through the inside of the ECA 134 via inputand output vents 132, 133. The internal air combines at the bottom ofthe ECA 134 for onward circulation over the front and rear of the LCDdisplays 121 as described above.

FIG. 2D shows a similar arrangement to FIG. 2A, but with a single LCDpanel 121, over which internal air flows in a loop as described above.At the opposite side of the housing 120, the internal air flows in asimilar loop that includes the space between the respective baffle 126and opposing wall of the housing 120. This is advantageous from a massvolume production perspective, enabling single and back-to-back displaysto share common design and manufacturing processes. Further designs maycomprise displays with housings divided internally into more than tworegions, each with or without a respective display panel, and a coolingmodule such as 100, 126 providing a flow of internal coolant through thecooling module and divided regions. In the example of FIGS. 2A to 2D,the baffles 126 serve as side walls of the cooling module andeffectively divide the housing internally into front and back regions.Alternative dividers may be employed.

Although it is advantageous for the baffles 126 to extend fully from oneside to an opposite side of the housing 120, a small amount of leakageat the sides of the baffles may be permissible, provided that the maincirculating loops of internal air, as described above, are maintained.The internal air from the main circulating loops mix with one anotheranyway, as they enter, pass through and exit from the cooling module100, 126. As shown in FIGS. 2A to 2D, the main circulating loops are notcompletely isolated from one another. Thus, there does not need to becomplete physical separation between the regions, provided that the maincirculating loops of internal air are maintained,

A first impelling means in the form of a series of fans 101 causes flowof the external cooling air through the rows 103. A second impellingmeans in the form of a series of fans 102 causes flow of the internalhot air through the columns 104. The first fans 101 are located at theinput side of the rows 103. The second fans 102 are located at theoutput side of the columns 104. Thus, in each case, the fans 101, 102are located at the cooler side of the heat-exchanger; this promotes alonger service life of the fans. However, the fans could be located atthe other sides of the rows 103 and columns 104.

As will be known to the skilled reader, in use of the heat-exchanger,heat is exchanged between the rows 103 and the columns 104 and thus theair flowing through them, so that the flow of external cooling airprovides cooling of the internal hot air, the effect of which is toraise the temperature of the external air as it passes through the rows103.

As indicated in FIG. 1, air flow through the rows 103 is substantiallyconstant at a rate N for each of the rows 103. Likewise, airflow throughthe columns 104 is substantially constant at a rate M for each of thecolumns 104. This is a typical arrangement for a crossflowheat-exchanger. Any suitable number of fans 101, 102 or other impellersmay be provided to cause the airflow.

A potential problem with this typical arrangement is that, in use, theheat-exchanger will tend to have hot and cold spots. As the externalcooling air travels from right to left, it gets progressively hotter. Asthe internal hot air travels from top to bottom, it gets progressivelycooler. Thus, at the top left corner of the heat-exchanger, heatedexternal air crosses hottest internal air: this is the hottest part ofthe heat-exchanger. The coldest part of the heat-exchanger is at thebottom right corner, where cooled internal air crosses coolest externalair.

FIG. 3 illustrates a temperature characteristic of a typical arrangementas above. Variables ix indicate variations of temperature of theinternal air, on a notional scale of x from 0 to 100, 0 being thecoldest temperature and 100 being the hottest. Variables ey indicatevariations of temperature of the external air on another notional scaleof y from 0 to 100, which will typically indicate different absolutetemperature values to those indicated by the scale ix.

Legends ix/ey indicate internal air and external air temperatures atintersections of the rows 103 and channels 104. Thus, for example, thecoldest spot at the bottom right corner gives a zero (coldest)temperature for both internal and external air—i00/e00. The highesttemperatures at the top left corner are indicated by i88/e88.

Relative temperature indications such as i00/e00 and i88/e88 alsoindicate a relatively low temperature differential between internal andexternal air and therefore a relatively low rate of heat transfer. Thisis the case wherever x=y, as tracked in FIG. 3 by the arrows from bottomright to top left corners. Diagonal dashed lines 105 indicate theboundaries of overall temperature bands that increase progressively frombottom right to top left.

At the top right corner of the heat-exchanger, indicated by i80/e08,relatively hot internal air (i80) and relatively cool external air (e08)have just entered the heat-exchanger so that there is a relatively hightemperature differential (i80-e08) between them, which indicates arelatively high rate of heat transfer—that is, most efficient cooling ofthe internal hot air. However, there is a relatively low temperaturedifferential at the bottom left corner of the heat-exchanger, whererelatively cool internal air crosses relative warm external air.

By way of a general, non-limiting example, for an ambient external airintake to the heat-exchanger of 20° C., the external air output of theheat-exchanger at the hottest point (e88) could be 30° C., where thetemperature differential of 10° C. has been exchanged with internal airwithin the heat-exchanger. Conversely, for an internal air input to theheat-exchanger of 60° C., the internal air output at the coolest pointcould be 48° C. (i00), where the temperature differential of 12° C. hasbeen exchanged with external air within the heat-exchanger. Forthermodynamic reasons, the temperature differential above may bedifferent for the different areas of the heat-exchanger e.g. top leftand bottom right. Furthermore, the temperature of the internal air maynot be uniform across all input channels of internal air to theheat-exchanger as a result of a) hot and cool spots of theheat-exchanger itself and b) solar loading differences on LCD displaysat the front and back of the display. Ambient external air temperatureis dependent on weather conditions and could for example drop to 0° C.,whilst internal hottest temperatures remain high e.g. 60° C. due tosolar loading heating the internal air. As shown in FIG. 3, the airtemperatures as the air traverses across the heat-exchanger will varyrelative to the associated input temperatures and the differentialbetween internal and external air within the heat-exchanger.

FIG. 4 illustrates how temperature differential varies over theheat-exchanger 100. In this figure, D indicates a nominal temperaturedifference between internal and external air streams. This temperaturedifference D obtains at all points where, in FIG. 3, ix=ey—indicated bya diagonal broken line 106. To the left of the line 106, heat transferefficiency decreases as the temperature differential decreases below thenominal differential D. To the right of the line 106, heat transferefficiency increases as the temperature differential increases above thenominal differential D. The changes in temperature differential areindicated by one or more minus (−) prefix and one or more plus (+)suffix. The more minus signs, the less the temperature differential. Themore plus signs, the greater the temperature differential. It mayreadily be seen that there is a considerable variation in temperaturedifferentials, from the bottom left-hand corner to the top right.

Thus, the further both internal and external airstreams travel into theheat-exchanger, the less efficient the heat exchange becomes as thetemperature difference between them reduces; where cool external airbecomes hotter, and as hotter internal air becomes cooler. When used tocool the LCD panel in an outdoor advertising screen, this can createvast temperature differentials across the surface of the LCD panel—e.g.in the above example, hot spots at the top left and cold spots at thebottom right. As LCD panels are sensitive to temperature and may fail tooperate in extremes of cold and heat, then such temperature spots are tobe avoided. This is applicable to many other applications.

FIG. 5 illustrates a first step in reducing the variations intemperature differential D over the surface of the heat-exchanger 100.

FIG. 5 is generally similar to FIG. 4, except that, in FIG. 5, the flowof external air through the rows 103 varies from row to row. This isachieved by varying the speeds of the fans 101.

In FIG. 5, the top fan 101 operates at normal speed to achieve a flowrate N. However, the next fan 101 below operates at a slower speed toachieve a flow rate N-a %. The next three fans 101 operate atprogressively slower speeds to achieve progressively lower flow ratesthat are less than N by b %, c % and d %.

This means that, as the hot internal air travels further down thecolumns 104 and is progressively cooled, the cooling, external airtravels at a progressively lower rate and therefore spends longer in theheat-exchanger. This increases the efficiency of the heat-exchange. Thevalues of temperature differential D for the top row 103 of theheat-exchanger remain as in FIG. 4, since the flow rates of bothinternal and external air are unchanged. However, in all lower rows 103,the temperature differential D is improved from top to bottom. In FIG.5, the qualifier ½ is introduced to indicate one-half of a full + or −measure, as the local value of D increases or decreases.

The temperature differential values D are improved further in FIG. 6,where the speeds of the fans 102 for the columns 104 are progressivelyreduced from right to left. Thus, the rightmost fan 102 operates atnormal speed to achieve a flow rate M. The speed of the fans 102 to theleft are then progressively reduced to achieve flow rates that are lessthan M by w %, x %, y % and z %. The values of temperature differentialD for the rightmost column 104 of the heat-exchanger remain as in FIG.5, since the flow rates of both internal and external air are unchanged.However, in all columns 104 to the left, the temperature differential Dis improved from right to left.

In fact, in FIG. 6, the lowest temperature differential D is now in thebottom left-hand corner and comparable to the normal value of D in FIGS.4 and 5. All other values above and to the right are improved.

The above describes an ideal scenario. However, environmental conditionsmay create variations from the ideal position e.g. as a result ofvarying temperatures across the different internal air input channels104 to the heat-exchanger and solar loading between front and reardisplays 121.

By way of example, referring to the values shown in FIG. 6, external fanspeeds may vary as follows a=20 (a 20% reduction of N), b=40, c=60,d=80; whereas internal fan speeds may be the same or different—forexample w=18, x=38, y=59, z=79.

The fan speeds may remain static for a period of operation or adjustedin a dynamic way during normal operation e.g. to account for varyingtemperatures across the internal air input channels of theheat-exchanger as a result of varying solar loading, both throughout theday and between front and rear LCD displays, as well as shading frombuildings, bus shelters, trees and other obstacles, particularly as thesun position moves throughout the day from dawn to dusk. Likewise, fanspeeds may be adjusted in a dynamic way to account for varying externalambient temperatures throughout the day or night. It is worth notingthat any changes to one or more internal fan speeds may or may notrequire changes to external fans speeds and vice-versa in order todeliver the require temperature differentials between associatedinternal and external air flow channels as a whole, across theheat-exchanger.

In FIG. 6, the speed of each fan 101, 102 may be controlledindependently by controllers 124 and 125 within the housing 120,responding to temperatures and/or other parameters measured on oradjacent the heat-exchanger and/or at other locations within the displayhousing 120. The controllers 124, 125 control the airflow through therespective channels to tend to maximise temperature differentialsbetween the internal air and the external air, at or around intersectionpoints of the rows 103 and columns 104.

As an alternative or addition to varying fan speeds, fans may beoperated at a fixed or predetermined speed and switched alternately onand off (e.g. by way of a variable duty cycle) to control the flow ofcoolant through the heat-exchanger.

By way of example, temperature sensors 107 are provided at or adjacentthe exits of the rows 103 and temperature sensors 108 are provided at oradjacent the exits of the columns 104. Sensors may be provided at otherlocations on the heat-exchanger 100. A respective temperature sensor107, 108 may not be provided for every row 103 or channel 104.

It will be appreciated from the foregoing that the illustrated examplesmay afford heat-exchangers that operate more efficiently and reduce thelikelihood of excessively hot and cold spots. This in turn may affordmore reliable operation of associated components, such as (for example)the LCD panel 121, electronics modules 122, fans 101, 102 and powersupply 123 as shown in FIGS. 2A to 2D. Improved reliability may beachieved directly by more uniform temperature distribution and byreducing the likelihood of condensation within the housing 120.

This may be particularly useful in the illustrated examples where, inpractice, there may not be a great deal of space for a largeheat-exchanger within the housing 120, the space of which may bedominated by one or more LCD panel 121. Thus, it is beneficial to have asmaller heat-exchanger of higher efficiency to fit the available space,as well as distributing temperature more evenly within the housing 120.

To summarise, greater heat-exchanger efficiency can be achieved byadjusting the air flow through each internal and external channel byadjusting the individual fan speeds. The internal and external air flowis reduced as the temperature differential between them lowers (i.e. asthe efficiency lowers) such that the internal and external air spendlonger in the heat-exchanger to aid heat exchange; This increasesefficiency in the respective areas of the heat-exchanger.

By adjusting the air flow across all internal and external air flowchannels (i.e. by adjusting individual fan speeds), then the efficiencyof the heat-exchanger as a whole increases; allowing greater heat to beextracted from the internal air for a given size of heat-exchanger.

Although slowing down airflow may reduce overall throughput of theheat-exchanger, the overall effect is to take more heat out of theinternal air, which heats up the external air for venting at the outputsof the external air channel side; the internal and external air volumesare in thermal contact through the heat-exchanger for longer, allowingmore of the heat to transfer.

The differential fan speeds (and related volume air flow) are adjustedrelative to each other to maximise the temperature differential withinthe heat-exchanger as a whole.

As an alternative to the illustrated examples described above, the fans101, 102 may be controlled in groups. A fan 101, 102 may cause airflowthrough a plurality of channels of a respective set. Airflow through thechannels may also or alternatively be controlled by respectiverestrictors for the channels, adjusted to achieve a desired rate offlow. Such restrictors may be preset to desired values or adjusted inuse by controllers. Such restrictors may restrict inlet and/or outletapertures to airflow channels, and/or the cross-sectional areas of theairflow channels may be adjusted.

Although the above-described and illustrated examples have beendescribed with reference to large-scale electronic displays,heat-exchangers may be deployed in wider applications such as heating,ventilation, air conditioning and cooling systems.

FIG. 7 illustrates sequences of operating states or processes of alarge-scale electronic display, which may be constructed as indicateddiagrammatically in FIGS. 2A to 2C. The following disclosure is of novelproposals for addressing condensation problems within such a large-scaleelectronic display.

As indicated in FIG. 7, the display is switched off completely by aPower Down process, which can be entered from any of the operatingstates. In order to switch on the display, it firstly enters a Power Upprocess and then proceeds via Cold Start and Warm Start processes toarrive at a Normal Operation state. From the Normal Operation state, itcan enter a Powersave state, during which it is effectively on standby.From that state, it may re-enter the Warm Start process to return to theNormal Operation state. The various states and processes are describedbelow. Firstly, however, potential problems arising from potentialcondensation are reviewed.

Outdoor electronic displays (as with many outdoor products) are builtfrom sensitive electronic components that may be subject to coldtemperatures. Condensation can occur on surfaces (e.g. metalwork andsensitive electronics) whose temperatures reach the prevailing dewpoint; where water held in warmer air converts to water on coolersurfaces at and below the dew point. Any water forming on sensitiveelectronics, as a result of direct condensation or indirect condensation(by dripping from e.g. a cold metal surface), can cause short circuits,corrosion, and build-up of mould or residue on electrical contacts andwiring that damages and prevents normal operation of the electronics.

In the following description, the term ‘metalwork’ is used convenientlyto refer to structural and other items within a display that havesignificant thermal mass, to the extent that they may have a surfacetemperature that lags behind any changes in in the temperature ofsurrounding air. In the context of large-scale electronic displays, amain chassis and any sub-chassis are typically of metal, so the genericterm metalwork is both apt and convenient. However, it is to beunderstood that, in the context of this specification, such structuraland other items may be of materials other than metal and term metalworkis to be construed accordingly.

For a given volume of air, raising its temperature reduces its relativehumidity (RH). This is referred to as Isobaric heating when pressureremains constant. Condensation is caused by the RH reaching 100%,usually as a result of a reduction in air temperature; but can also becaused by a reduction in air pressure (Isothermic compression). Thepressure will be assumed to be constant for the purposes of thefollowing.

Dew point may be defined as the temperature to which air must be cooledto become saturated with water vapour. When further cooled, airbornewater vapour will condense to form liquid dew. Or dew point may bedefined as the temperature at which a given volume of air with specificmoisture content will reach 100% RH and condensation will occur.

There is a known simple approximation that allows conversion between thedew point, air temperature, and relative humidity; which is accurate towithin approximately ±1° C. (providing the relative humidity is above50%). This is:Tdp≈T−((100−RH)/5)RH≈100−5(T−Tdp)

Where RH=Relative Humidity (%); Tdp=Dew Point Temperature (° C.); T=Airtemperature (° C.)

This shows that as the RH approaches 100%, then the dew point approachesthe air temperature. It is desirable to both raise Air Temperature andlower Relative Humidity (RH) for a given volume of air. More complex andaccurate calculations exists such as the Magnus formula and Arden Buckequation.

When outdoor electronic displays are first installed or are serviced,there is often a delay between the physical installation or servicingand the application of power to energise the display. Where a displayunit is cold and relative humidity is high, it is susceptible tointernal condensation on sensitive electronics that both control andinclude the backlight of an LCD panel or the like. An LCD backlighttypically provides a significant source of heat generation within adisplay; increasing its brightness typically increases the heat of thesurrounding (internal) air and increases surface temperatures within thedisplay. This in turn raises the dew point such that condensationevaporates; which is then held within the air within the display. Thewarmer the temperature, the lower the relative humidity.

Applying power to sensitive electronics when the display unit is coldand relative humidity is high is at risk of causing problems due tocondensation—but without powering on the electronics, then the backlightcannot be turned on to generate the necessary heat to reduce RH andcondensation. Thus, we have appreciated a need to heat the display unitquickly to reduce relative humidity and raise the dew point such thatair circulating within the unit has lower relative humidity and is thusless likely to condense onto cold surfaces—which are typically metalwithin a large-scale display but could be of other materials.

Cold air brought into the external air side of a heat-exchanger within adisplay unit is progressively heated as its traverses across theheat-exchanger to the outlet, as internal heat is exchanged to cool theinternal temperature within the unit. Any cold morning air brought intothe unit, via heat-exchanger air intake fans, cools internal surfaces toform cold spots and creates the possibility of internal condensation onsurfaces that come into contact with warm humid internal air. Thiscauses the temperature of the local air around the cold spot to belowered, raising RH that then causes condensation on the cool surface asthe dew point is reached.

If internal circulating air is cool (e.g. after a cold start), thenthere is very little temperature differential between the internalcirculating air and the localised external air around the cold spot(which can thermally conduct to the internal area), so that RH may morequickly reach 100% and cause high levels of condensation. We havedetermined that, by pre-heating the internal air as quickly as possibleand as hot as possible (within operating limits of the internalcomponents) this creates a larger temperature differential between thedew point of the localised cold spot (as a result of thermal conductionfrom the external cold air) and the internal circulating air, resultingin lower RH and lower risk of condensation. The hotter the internalcirculating air gets around the cold spot, then the more thecondensation evaporates. Conversely, the greater the volume of cold airthat persists in the external air flow, which thermally conducts to aninternal surface, then the greater the cooling effect on the local airaround the cold spot and the greater the condensation.

If internal surfaces of the display unit are already hot (warmed up)then there is a greater temperature differential with the external coldair and the area of the “localised cold spot” will be reduced. Howeverif the internal surface is cold, then the external cold air will furthercool the internal surface and increase the area that will generatecondensation (due to the lower temperature differential) and create amuch wider area for the internal “cold spot”, which will have a muchgreater cooling effect leading to much greater RH and associatedcondensation. With cold metalwork or other surfaces, and incoming coldair from the heat-exchanger, then the internal temperature as a whole issusceptible to lowering quickly and raising RH to cause condensation.

Cold air input from the heat-exchanger therefore needs to be controlledto avoid “over cooling” of the internal air steam as the metalwork getsup to full heat. The internal metalwork or other surfaces need to beheated sufficiently to prevent thermal conduction from outside causingcondensation, before bringing cold external air into the heat-exchanger.

Complex temperature control and management is therefore required to heatup the display unit as quickly as possible but minimise the risk ofcondensation by bringing in cold air into the unit that conducts tocreate cold spots at or below the dew point on internal metal or othersurfaces; combined with bringing in sufficient cooling to manage hightemperatures to prevent the unit from overheating as a result ofbacklight brightness levels and solar loading.

Although measures can be taken to reduce moisture content withininternal air e.g. using silica gel, external moisture can re-enter thedisplay unit when the door is opened (e.g. for servicing), which leadsto the need to manage relative humidity, temperature and associatedcondensation on an ongoing basis.

A heat-exchanger typically uses numerous input fans that are enabledtogether to draw external air through the heat-exchanger. Since fanshave a minimum speed to operate, when enabled together this may pull toomuch air through the heat-exchanger that “over-cools” the internal airflow as the unit comes up to full heat (i.e. metalwork heats up toprevent the cool air causing condensation).

Sensitive electronics such as PCs, power supplies, video electronics canbe “hardened” to be less/non-sensitive to moisture, using knowntechniques such as conformally coating the surface of the electronicswith a moisture repellent material or “potting” the electronics within awaterproof resin. This is the meaning of the term “hardened” in thisspecification. However these methods are expensive and hindermanufacture and repair of electronic assemblies once applied, oftenrendering the assembly unrepairable, requiring full replacement ifproblems arise, thereby incurring additional costs.

Thus, we have appreciated a need for an apparatus and a method thatallows a large-scale electronic advertising display to be started undercold conditions where temperature and humidity can be managedeffectively, without causing humidity/condensation issues whilst theunit gets up to full operational conditions. Preferably, once anelectronic display has been brought up to full operational conditions,its temperature and humidity can be controlled at an optimum level.

Likewise, if an operational electronic display unit is powered down orplaced into reduced e.g. “standby” operating modes (e.g. overnight),then there is a need to manage the temperature, humidity andcondensation to bring the unit back up to full operation e.g. in themorning.

Humidity/moisture issues are compounded for field serviceable equipment,as moisture can re-enter the unit when the door is opened. By managinghumidity centred on dew points, this may obviate the need to seal andservice units in environmentally controlled environments for ease ofrepair in the field.

The coolest part of a heat-exchanger in an electronic display unit istypically at the external air intake side (i.e. bringing in ambient coldair) where it meets with already cooled internal air at/towards theinternal air output—that is, where the temperature differential betweeninternal and external air is least at the cold external air input. Thus,this location is most at risk from developing condensation internallywhen first bringing cold air into the unit, when powering up in coldenvironments. Any condensation developing on internal metalwork of theheat-exchanger in this area is at risk of dripping onto sensitiveelectronics below.

Understanding the dew point in this area is important, to ensure that nocondensation is formed as a result of turning on the heat-exchanger fansto bring in cold air, for example by:

direct measurement of dew point from temperature/humidity sensorsmounted on metalwork (or other surface) of the heat-exchanger; and/or

calculation/prediction/inference by measurement of temperature/humidityin air flow within the external air path at both input (i.e. ambientexternal air) and output (exhaust) of the heat-exchanger; and within theinternal air path at both input and output of the heat-exchanger.

It is useful to determine ambient (external) temperature in order tobest control how much cold air external fans bring into theheat-exchanger. However, it is difficult to detect this when atemperature sensor is placed within a display, as ambient temperaturecan only really be measured when the external airflow fans are runningin order to draw ambient air across the sensor. Without turning onexternal fans, the sensor may measure heat radiated from theheat-exchanger i.e. an internal temperature.

Management and understanding of dew point is therefore important whencold starting a display unit in a cold environment to ensurecondensation is not generated by the heat-exchanger as a result ofrunning the external fans for too long.

It is worth noting that condensation is “distilled water”, i.e. it hasbeen distilled to water from the air. Distilled water (in liquid form orwhen frozen) is a very poor conductor. If condensation forms (or drips)onto high-voltage circuits such as AC mains power supplies, then it maycause protection circuits to trip e.g. where there is an earth leakage.If the environment is such that there is risk of condensation, then itis preferred to protect high voltage/mains circuits from condensatione.g. by choosing IP67 or IP68 rated components, sealing, conformallycoating, potting, partially potting, covering or restricting air (thatcarries moisture) around the sensitive AC components.

If condensation forms on low-voltage electronic circuits e.g. 12 Volt DCor 5 Volt DC, then there is a very low risk of the condensation causingshort circuits on first (or low) exposure. However condensation causesmetal surfaces (e.g. semiconductor, connector pins etc) to rust andprematurely age over time, particularly where there is continued/regularexposure. As condensation then forms on aged/rusted low voltageelectronic circuits, the condensation picks up impurities fromrusted/aged metal as well as atmospheric contamination, dust etc whichincreases the conductivity of the condensation. Low-voltage circuits aretherefore more prone to short circuit issues (and open circuit issues asmetal paths deteriorate) related to condensation over a longer period oftime (compared to high voltage circuits where currents are much higher),as the impurities build up over time.

During initial power up conditions (where a unit has been powered offand exposed to a cold ambient environment for a period of time), we havethus appreciated that desirable requirements are to: protect (“harden”)high voltage electronics to prevent shorts and earth leakage; andminimise the frequency that cold start conditions arise (where there isincreased risk of condensation) to prevent build-up of impurities on lowvoltage circuits to prevent open and short circuits.

We have appreciated that there are four distinct operational stateswhere humidity and related condensation need to be managed (based on dewpoint) within outdoor, large-scale electronic advertising displayunits—and other equipment with a heat source. These are illustrated inFIG. 7.

Cold start—where the unit has been off for a period of time and it hasnot been able to maintain a desired internal operating temperature—lowtemperatures yield high RH. Care needs to be taken before applying powerto moisture sensitive components (such as a controlling PC within theunit), which are required to manage the system as a whole. Pre-heatingand dehumidification can ensure that environmental conditions areacceptable before starting and passing control to the PC.

Warm start. In an electronic display unit, an LCD panel (or the like)tends to be the most environmentally sensitive of the electronics. Thus,care needs to be taken to ensure that there are no cold spots at or nearthe LCD panel before turning it on. Warm Start is the process of turningon the LCD panel after the correct environmental conditions have beenachieved and setting the initial operating temperature high to aid quickwarming up of the metalwork (or the like), in order to minimisecondensation as external heat-exchanger fans are first turned on. Itoccurs following either of two related processes, namely:—

-   -   After Cold Start. In this case, Warm Start can be considered as        an extension to Cold Start, where the PC (having been sequenced        ON when environmental conditions permit) manages the turning on        of the LCD Panel before entering Normal Operation, centred        around an initial high start-up temperature; and    -   After exiting “Powersave” (where the backlight is powered off        during non-advertising hours) to enter into normal operational        mode, by powering up the LCD panel—typically when appropriate        environmental conditions exist at dawn (or retail store opening        time), before entering Normal Operation, centred around an        initial high start-up temperature

Normal operation, which aims to maintain a constant internal temperatureat desired levels by adjusting cooling air flow in response to heatgenerated by both the LCD backlight and solar load. Under normaloperating conditions, the internal temperature level will be “NORMAL”e.g. 20 degrees C. However it may be raised to a HIGH level e.g. 40degrees C. after (1) WARM START (to warm up the metalwork, as described)AND (2) As a pre-emptive measure to retain heat (by taking in lesscooling air) when cooling down (e.g. at night) to delay the possibilityof turning on a heater during Powersave. Temperature management will beparticularly sensitive to bringing in external cold air through theheat-exchanger to avoid condensation forming; and ensuring thattemperature and RH are managed at acceptable levels.

Powersave, where the LCD panel and backlight are turned off outsideadvertising hours (typically overnight). When the backlight is turnedoff, the temperature drops and RH rises (even with externalheat-exchanger fans off); and metalwork starts to get cooler. It isdesirable to monitor temperature/humidity and prevent the humidity fromrising to unacceptable levels that risk dew point (e.g. 50% RH) on thecold metal. The display may comprise a primary heats source and thebacklight can be used as a secondary heat source—e.g. turned on with thescaler off, so no content is displayed—to help maintain an acceptabletemperature and RH level. Upon exiting the Powersave process, it isimportant to re-enter the Warm Start process to manage cold air intake.

Elements for use in examples of apparatus and methods, as part of aprocess (in part or whole) to bring an outdoor, large-scale electronicadvertising display unit into normal operation, include the following:—

1. Sensors

When the unit is off for a period of time, the temperature of the unit(and mass of metalwork) will track ambient temperature. Temperature andhumidity sensors are placed around the inside of the unit to helpdetermine dew point within the unit that may cause condensation. Inparticular, a temperature/humidity sensor is positioned directly on themetalwork of the heat-exchanger at the coldest location (see earlierdescription) susceptible to condensation. This is the location at mostrisk for generating condensation as a result of thermal conduction fromthe external cold air to the internal metal surfaces and surroundinglocalised air, which may then cause additional cooling (beyond theheat-exchanger's normal function) that raises the internal RH.Condensation occurs as the RH reaches 100% when the internal air comesinto contact with the cold surface of the heat-exchanger at or below thedew point temperature.

Optionally, as the heat-exchanger starts to warm up, an external fan mayneed to run briefly to draw ambient air in and across atemperature/humidity sensor within the external airflow at the entranceto the heat-exchanger.

Temperature and humidity sensors are initially monitored and managed bya power management board (PMB) to aid the Cold Start process; andsubsequent monitored and managed by the sensitive electronics (e.g. PC)on completion of the Cold Start process.

2. Non-Sensitive Control Electronics (Power Management and AssociatedPower Supply)

Dedicated embedded electronics are hardened to work under coldenvironmental conditions and can be first powered to control initialstart-up, including 1) power management control board (optional) and 2)12 v power supply. These items may comprise analogue or digitalelectronics.

The electronics may be hardened through choice of electronic componentsdesigned to operate in cold/moisture environments; and or conformalcoating; and/or potting within resin; and/or selection of IP67/68 ratedcomponents or assemblies; and/or other known hardening methods thatallow a power management board PMB and associated power supply unit PSUto operate.

The power management board PMB may be capable of reading sensors,carrying out decision making and controlling power to other devices e.g.heater, dehumidifier and sensitive control electronics e.g. PC, video,LCD driver electronics. Environmental control is passed to the sensitivePC when finally powered, which can then continue sequencing on furthersensitive electronics such as the LCD panel, through the Warm Startprocess

3. Heater

Initial use of one or more heater under cold conditions may becontrolled from a power management board, such that the heater is turnedon when the environment (temperature, humidity, dew points) are notsuitable for starting sensitive electronics.

The heater will raise the internal temperature and lower the RH to helpprevent condensation on cold surfaces at the dew point.

The heater can be turned off once sensitive electronics have beenpowered (enabled by the power management board), whereupon fullenvironmental temperature control is then passed to the sensitiveelectronics—e.g. a PC.

4. Dehumidifier

Use of a dehumidifier under cold conditions may be controlled initiallythe power management board. The dehumidifier is turned on when theenvironment (temperature, humidity, dew points) are not suitable forstarting sensitive electronics. The dehumidifier removes water contentfrom the internal air and transfer it to outside of the enclosure of thedisplay unit, to further reduce RH.

Control of the dehumidifier is passed to the sensitive electronics onceit has been powered on; if required, the dehumidifier may be left onwhilst the full Cold Start process completes. It may also be turned onuntil all water content has been removed or falls below an acceptablelevel, to aid the lifetime operation of the dehumidifier and/or display.The dehumidifier may be re-enabled if RH increases above an acceptablelevel—e.g. as a result of exposing the internal sensitive electronics toambient air as a result of opening a door of the display unit or due toa breach of door seals.

The dehumidifier may run continuously until RH is below a pre-setacceptable threshold; especially as the use of an hydrophobic filter(e.g. a Gore vent) that equalises internal and external air pressure mayintroduce additional humidity from external ambient air on an ongoingbasis—i.e. the unit is not fully hermetically sealed from externalambient air

5. Sensitive Electronics Control of Backlight for Heat Generation

As a backlight for an LCD panel (or the like) typically generates heat,it can serve as a controlled heat source for the display unit, thecontrol being provided by sensitive electronics of the unit, once theelectronics has been enabled. Such electronics may typically comprise aPC, LCD display, video circuits, power supplies, high voltage driversand so on—any other restricted temperature/humidity range products thatare not treated for use in cold environmental conditions, and which areenabled once satisfactory environmental conditions have beenestablished.

Once enabled, the sensitive electronics may also control operation ofany other heat source within the unit.

6. Managed Heat-Exchanger Start Up (Individual Fan Control/BurstOperation)

Individually controlled internal and external fans (e.g. 1-5 in number)control how cold air is introduced into the system. The fans areselectively turned on as the display unit heats up in a way thatminimises risk of condensation. They are managed in a relative ratiothat permits efficient heat-exchanger use to deliver a substantiallyconstant internal operating temperature.

They are selectively turned off as the display unit cools down in a waythat minimises risk of condensation.

Building on the preceding description, FIG. 8A illustrates a Cold Startoperation of a large-scale electronic display unit. The process may beunderstood by following the flowchart of FIG. 8A.

Cold Start occurs every time the unit is powered up and ensures thatsufficient temperatures and dew points are achieved to successivelyenable environmentally sensitive electronics (within their associatedenvironmental specification).

A Power Management Board PMB that is itself optionally hardened ispowered up from a hardened 12 V PSU. The PMB turns on an internal heatsource to generate heat before any other electronics are enabled, inorder to pre-heat the internal air; which will reduce RH within theinternal air.

The heated internal air will circulate naturally through convection, byfirstly rising as it becomes hot, cooling against glass at the front ofthe display and then falling to the bottom of the unit to initiate aconvected circulating air flow. One or more small 12 v fan may be usedto help guide circulating air across sensors etc.

The convected circulating air temperature and humidity is sampled; andwhen reaching acceptable levels then the PMB turns ON a CAN bus (as oneexample of an industrial Multidrop or Fieldbus network for datacommunication), which then allows the PMB to communicate with furthercontrol and measurement electronics within the unit. Temperature andhumidity levels may be measured directly in real time, or a pre-heat“time period” may be predetermined through a previous characterisationof the unit or PC based thermal modelling.

The PMB may then turn on a dehumidifier, if provided. The dehumidifiercould optionally be turned on earlier if connected directly to the PMB.

The PMB will turn on internal circulating fans to more efficientlycirculate internal air through a heat-exchanger of the unit although, atthis time, external heat-exchanger fans will remain off.

Where appropriate, further temperature and humidity sensors readings canbe taken to ensure that the pre-heat internal temperature is stable, tominimise RH.

When temperature and humidity reach acceptable levels, the PMB turns ona PC and Router of the unit (which are more sensitive than CAN buselectronics), enabling the PC to take further control of managing theenvironmental conditions.

The PMB will then relinquish being master of the CAN bus, so that the PCcan then control and monitor all electronics connected to the PC CAN buse.g. sensors, fan control. In particular, the PC can then manage (aspart of the subsequent Warm Start process) the turning on of the LCDpanel which is typically the most sensitive part of the display unit.The PC will also control the initial heat source, if needed further.

It may be noted that internal circulating fans and associated CAN buselectronics can be turned on sooner or immediately if they are“hardened” to withstand the environmental conditions (e.g. conformallycoated to prevent condensation issues). However, this approach will tendto provide lower cost benefits.

The process of FIG. 8B is similar to that of FIG. 8A, except that,instead of initially measuring temperature and humidity levels directlyin real time, a pre-heat time period is predetermined through a previouscharacterisation of the unit or PC based thermal modelling.

With reference to FIG. 8B, when the heat source is initially turned on,convected air circulation is slow, without fan assistance. Under thefollowing preferred conditions, the start-up time for completing theCold Start process can be shortened by providing the conditions to turnon the internal circulating fans sooner rather than later, to moreeffectively distribute internal heat within the air. The preferredconditions are:

-   -   Fan power supplies are hardened (IP67/68 rated, covered,        semi-potted, etc to protect from condensation), as well as the        12 v PSU; There is a temperature controlled environment when        fully operational, such that low voltage circuits have minimal        exposure to condensation over time;    -   Infrequent power cycling during operation such that the cold        start process is entered only for installation or maintenance        purposes; and Low voltage circuits (e.g. PMB, CAN bus        components) utilising electronic components specified for the        environmental temperature range, noting that these do not        necessarily need to be hardened (through conformal coating,        potting, sealing etc) due to the purity of condensation        (distilled water) and minimal exposure to condensation (i.e.        impurities) given the preceding conditions.

The PMB turns the heater on, but waits for a period of time to pre-heatthe internal air before then turning on the internal fans (via the CANbus) to circulate the warmed air. The CAN bus electronics are lowvoltage, enabling monitoring of all sensors and control of all fans etc.The warm air will be circulated until the temperature and humidityconditions are acceptable for the PC and ROUTER to operate.

Once the PMB has successfully started the PC it will relinquish the SCANbus master, allowing the PC to take control of the environmentalmanagement; and to then get the display unit into Normal Operation viathe warm start process, which ensures the environmental conditions forturning on the LCD panel are achieved before turning on the LCD panel.

The PMB could optionally manage the environmental conditions to controlthe LCD panel into Normal Operation). However, it is preferred to getthe PC operational as soon as possible, as it typically has far greaterprocessing power and has prime responsibility for operationalenvironmental management. Also, the PC needs to manage the LCD panelthrough Warm Start after completing a Powersave process where the LCD isturned off. Warm Start can be considered as part of Cold Start whenprocessed for the first time.

In the optional variant of FIG. 8C, the heater is controlled as a deviceon the CAN bus, rather than being connected directly to the PMB. Thus,the PMB turns on the CAN bus upon power-up and immediately turns on boththe heater and the internal circulating fans without pre-heating theinternal air.

This may be required in some heater physical positions (e.g. towards thetop of the unit) where pre-heating air only heats the top of the unit,and where circulating convected air cools down too much against coldglass to leave the bottom of the unit remaining cold.

Heated air at the top of the unit will absorb moisture into the air. Ifthe heated air is then circulated to a cold area at the bottom of theunit it may condense on surfaces in this area that are at or below thedew point. In this case, it is therefore advantageous to turn on thecirculating fans at the same time as the heater in order to absorb andmanage condensation throughout the unit as a whole by distributing heat.

By placing the heater on the CAN bus, it allows the PC to control theheater directly, rather than via the PMB, for subsequent management ofhumidity and temperature, once the PMB has relinquished control of theCAN bus when the PC has been started.

Features and advantages of using a CAN bus are now discussed. CAN(Controller Area Network) bus is a multidrop bus network protocol thatis used widely in the automotive industry.

Digital displays used for advertising purposes have traditionally beendeveloped from PC based technologies. Consumer grade LCD displays wereoften used that were limited in size as a result of availability fordomestic consumer applications e.g. 24″, 32″, 40″ (61, 81, 102 cm). As aresult, display technology has evolved around a central processing coree.g. PC with point to point connections to display, fans and sensors;and/or short multiplexed serial connections to local sensors e.g. usingI²C, a multidrop bus designed for chip-level working, rather thanconnections between separate assemblies.

As larger display technology has become increasing commercially viable,connections between the central processor e.g. PC and sensors and otherinput/output devices have remained point to point; such the central PCcore is in control of reading the input devices, processing and managingoutput devices directly. Longer wiring lengths are less immune toelectrical noise e.g. from larger fans that are needed to cool largerdisplays; as well as being a source of noise for other devices. Ascooling and thermal management becomes an increasing issue for largerdisplays (and associated backlights), then the more challenging the airflow management also becomes as space gets restricted, particularly asmedia clients desire cosmetically slimmer screens. Routing multiplepoint-to-point cabling between central processing units and sensorsdistributed within a display provides barriers to air flow.

The use of a multidrop bus, such as a CAN bus, mitigates these issues bydecentralising immediate processing of “dumb” input devices (e.g.sensors) and output devices (e.g. fans) from the central processingunit; by distributing the intelligence locally to the desired vicinityof the device by making the input/output device intelligent e.g. using alocal microcontroller, such that it does not need to be immediatelyprocessed by a central processing unit in real-time.

Whilst internal networks such as Ethernet have been used to network PCand router elements, this networking technology is not cost effective ormulti-drop for networking the input/output devices to a PC for higherlevel management.

There are benefits to integrating multiple input sensors and/or controloutput devices with a common microcontroller to provide multifunctionintelligent input/output modules that can be distributed at locationsaround a large digital advertising display to perform both specific andvaried functions; dependent upon the monitoring and control requirementsat specific locations within and/or attached to the electronic display.Example intelligent I/O modules include:—

-   -   Environment Module—integrating temperature, humidity and light        sensors with a common microcontroller that provides CAN bus        connectivity to other intelligent I/O modules and a central        electronic processor e.g. PC    -   Fan Control Module—integrating PWM fan speed control outputs,        dehumidifier control outputs as well as fan speed, temperature        and humidity sensors with a common microcontroller that provides        CAN bus connectivity to other intelligent I/O modules and a        central electronic processor e.g. PC    -   Display Module—integrating video and backlight output controls        as well as video loss/presence detection, temperature and        humidity sensors with a common microcontroller that provides CAN        bus connectivity to other intelligent I/O modules and a central        electronic processor e.g. PC    -   Power Switching Module—providing power switching to various        elements e.g. backlight, heater as well as other monitoring        functions such a door open/closed contacts    -   Power Management Board (PMB)—providing an interface to a central        electronic processor e.g. PC, enabling the PC to interface with        the CAN bus network to provide central processing control of all        distributed intelligent I/O modules via the CAN bus network.    -   Typically:        -   The PC interfaces to the PMB via a USB port        -   Any high level Master/Slave/Notification protocol used to            transfer data between the electronic processor and            distributed I/O modules is encapsulated within its own data            link transfer protocol to provide a resilient way of            communicating between the PC and the PMB        -   The microcontroller on the PMB bridges the high level            Master/Slave/Notification protocol between the USB            connection (to/from PC) and the CAN Bus (to/from distributed            I/O modules)        -   Thus allowing the electronic processor (master) to poll a            specific I/O module (slave) using a destination address that            matches the I/O module's allocated Identifier address; set            as part of a self-configuration address process detailed            herein.

Examples of multiple functionality (dependent on location) include:—

-   -   A common Environment Module that can        -   attach to and/or process inputs from different sensors e.g.            an ambient light sensor or an RGB light sensor that senses            light output from the front face of an LCD display        -   be positioned at/near the top of the LCD display to measure            RGB light from the front face of the display, as well as            specific temperature and humidity environmental conditions            in this hotter area of the display        -   be positioned at/near the bottom of the LCD display to            measure ambient light, as well as specific temperature and            humidity environmental conditions in this cooler area of the            display        -   Be positioned at the top and bottom of multiple displays            e.g. back-to-back displays        -   Be positioned in other areas e.g. hot spots, cold spots etc,            where environmental conditions need to be managed as part of            a thermal management control system.    -   A common Fan Controller Module that can        -   Be positioned near and control heat exchanger internal            airflow fans        -   Be positioned near and control heat exchanger external            airflow fans        -   Monitor associated fan speeds on internal or external fans        -   Measure associated temperature and humidity within            associated internal or external air flows        -   Control other devices e.g. dehumidifier if available at the            specific location.    -   Other repurposed intelligent I/O modules may optionally include        and allow other varied sensors to be attached dependent on their        location e.g. shock sensors, tilt sensors, door sensors, energy        sensors via common means e.g. contact closures, pulse counting        etc; where the input signal is conditioned/processed in a        suitable manner e.g. de-bounce signals, pulse counting and where        necessary carry out alarm processing for notification to the        central electronic processor e.g. PC.

Multifunction capability is enabled by allowing different operatingsoftware/firmware to run on the microcontroller that is specific to thefunction required for the desired location. This can be facilitatedthrough a self-configuration addressing process as follows:—

-   -   Providing an input configuration to the intelligent I/O module        that can be read by the microcontroller, e.g.        -   Selectable switches e.g. DIP switches        -   Jumper settings        -   Configured on the cabling/wiring to the intelligent module            at the specific location        -   Hardcoded within the microcontrollers software/firmware        -   Other means e.g. dynamically assigned by central electronic            processor or configuration tool etc.    -   The microcontroller selects and runs built-in desired operating        software or operating mode dependent on the configuration        selected    -   The microcontroller maps the input configuration into a CAN bus        unique identifier (in whole, part or through cross-referenced        look-up translation) that allows the intelligent I/O module to        -   Be uniquely identified on the CAN bus by all other            intelligent I/O modules and the central electronic processor            e.g. PC        -   Provide a higher level addressing means (above the standard            CAN Bus ISO model (layer 2) datalink layer) so that the            specific intelligent I/O module to be uniquely addressed as            a “destination” “slave” by a “master” device e.g. central            electronic processor e.g. PC for higher level data            communication purposes over the CAN bus        -   Noting that the input configuration for both multifunction            operating mode selection and CAN bus identifier selection            can be a common or separate configuration means.

A modular/distributed approach provided by a multidrop bus combined withmultifunction/self-configuration addressing functionality isadvantageous on many levels e.g.

a) Allowing a common “Input/Output Device” to be used in multiplelocations e.g. an intelligent temperature/humidity sensor that can bepositioned in various distributed locations e.g. heat-exchangermetalwork, at internal air inlets and outlets of heat exchanger and, forexample, all other locations identified in FIG. 11.

b) Provision can be made to extend the CAN bus for use with other add-onassemblies and input/output accessories, that when integrated with, forexample, an Outdoor single Advertising Display Assembly create new andextended products where input and output devices are distributed acrossvarious combinations of assemblies. The multidrop bus may be used as anexpansion means but where external modules can operate eitherautonomously (where intelligence is distributed) or under direct controlof a main processing unit within the outdoor display.

Examples include:

-   -   Back-to-back advertising display, where the CAN bus is extended        to manage other input sensors and output components associated        with an additional LCD display;    -   A range of ‘Smart City’ products that integrate accessories such        as:    -   Environmental monitoring e.g. by utilising the CAN Bus to        communicate with CO₂ sensors, pollution sensors, air quality        sensors, weather sensors, noise sensors, pollen sensors, etc;    -   Electric car charging stations e.g. by utilising the CAN Bus to        communicate with payment systems, detect payment and control        actuators to enable electric car charging;    -   Wayfinder touch screens to detail local services;    -   Telecommunications equipment, including smart telephone boxes;    -   Car park payment systems.

c) Enabling the physical design of a display to be cosmetically changedeasily; such that distributed modules can be physically relocated withina housing.

d) Expandable—e.g. to add easily additional nodes/sensors on the bus.

A resilient multidrop bus provides a convenient means of locallynetworking intelligent Input/Output devices to a central processor;allowing

a) Reduced wiring as common I/O devices share a common multiplexed bus;

b) a microcontroller to be close to an associated input sensor or outputcomponent, the microcontroller processing associated data independentlyfrom a central processor; and

c) communication of digital data between distributed microcontrollersand a central processor.

CAN bus is particularly advantageous since:

-   -   It is very robust and is designed to operate in electrically        noisy environments    -   It is hot swappable allowing I/O devices to be plugged in/out of        the bus whilst powered.    -   It automatically manages contention of the shared bus (e.g. if        two devices communicate simultaneously) in hardware, requiring        no software overhead    -   It automatically manages error correction e.g. as a result of        noise, in hardware requiring not software overhead    -   It automatically manages device identification without prior        pre-programming; again reducing software overhead    -   CAN bus is a cost-effective solution, particularly since both        Physical Layer (ISO layer 1) and Data Link Layer (ISO Layer 2)        (including Transfer layer and Object layer) are implemented in        hardware and integrated within many low cost microcontrollers.    -   Data can be driven over long distances in digital displays,        without error, providing ideal communication with sensor nodes        distributed over a wide area.    -   CAN bus allows the nodes to operate autonomously such that the        nodes are able to transmit messages as real-time events arise        e.g. temperature exceeds a configured threshold    -   CAN bus allows nodes to transmit messages at any time, where bus        access is granted to the message with the highest priority, with        automatic management of bus contention    -   CAN Bus can automatically disconnect any faulty nodes such that        it does not prevent other nodes communicating, such that the        network as a whole is more fault tolerant than other multidrop        or field bus protocols.    -   CAN Bus is expandable, to easily add additional nodes and        devices on the bus.

It is worth noting that, in a conventional CAN bus implementation, whena node sends a message on the CAN bus, then all nodes receive themessage—i.e. the message is broadcast to all nodes on the CAN bus. CANbus addressing is arranged so that a node (with an identifier) transmitsits data to all other nodes on the CAN Bus. There is no specificdestination address specified in the CAN bus message to identify thedestination node, since it operates on a peer-to-peer basis where allnodes receive messages with optional filtering implemented in CAN Bushardware at the Object layer; so that one or more other nodes can act onthe data. This allows all nodes to transmit data at the same time toother nodes that are required to act on the data, with the CAN Bushardware managing any potential data collisions. Whilst this providessignificant benefits for truly distributed processing systems e.g.automotive and industrial control; it does provide limitations andchallenges for large outdoor digital displays that need to be overcome.

Large digital displays operate complex closed loop control thermalmanagement systems that control fans/cooling systems in response tomultiple heat sources including ambient light, display/backlightbrightness, ambient temperatures, internal temperatures at numerousvarious hot and cold spot locations as well as controlling heaters tomanage humidity.

Whilst native CAN Bus has the ability to enable fans to autonomouslycontrol fan speed in response to individual temperatures, it ispreferred that the complex closed loop calculations are carried outcentrally, and this requires a system, usually PC based to

-   -   Monitor associated temperatures, humidity at multiple varied        locations; as well as current fan speeds,    -   Calculate desired fans speeds as part of a close loop system,    -   Control the internal and external heat exchanger fans to achieve        the desired internal environmental conditions.

In addition, there is also a requirement to respond quickly toexceptions and alarm conditions as they occur, such as loss of mainspower, loss of video signal, reset requests (e.g. remote), door openedetc.

In order to manage numerous and distributed “slave” intelligent I/Omodules from a central PC “master”, it is preferred that the CAN Bus isadapted to support higher level “destination” addressing and“Command/Response” functions, currently outside the CAN Bus Data LinkLayer, through a higher level data communication protocol that supports:

-   -   POLLING (MASTER/SLAVE) MODE—where the central MASTER e.g. PC        polls each slave e.g. Intelligent I/O module to request and        gather conditioned input data e.g. temperature and set desired        output conditions e.g. fan speed.    -   NOTIFICATION MODE—where any slave intelligent I/O module can        communicate directly with the MASTER or other devices, without        waiting for the MASTER to POLL it e.g. to notify immediately        upon        -   Loss of power        -   Loss of video        -   Door open        -   Remote reboot        -   Watchdog time out        -   Node boot up        -   Etc    -   A standard CAN 2.0B message frame defines    -   A header within the protocol consisting of an Identifier (11        bits) and Identifier Extension (18 bit); which is used by a node        to identify itself and associated data to all other nodes on the        CAN Bus Network.    -   As well as associated Data fields for the communication of        associated data, and    -   Other framing data for start of frame, end of frame, CRCs and        synchronisation characters.

Whilst the standard Identifier is configured as part of theself-configuration addressing process to identify the source node (e.g.TOP Environmental Module on the front display, Internal Fan ControlModule etc); the following additional information is required to betransferred within a higher level protocol within the CAN Bus messageformat in order to permit the Master/Slave mechanism:

-   -   Destination Address (e.g. 11 bits)—that the source node would        like to transfer its data payload to    -   Function (e.g. 7 bits)—that it would like the destination node        to carry out e.g.        -   COMMANDS from a MASTER node e.g. read inputs, set outputs,            set configuration        -   RESPONSES from a specific SLAVE NODE e.g. requested input            data, acknowledgement of completing the requested command,            error conditions, etc        -   NOTIFICATIONS of alarm conditions e.g. loss of power,            supervisory states e.g. node boot up

The additional Destination Address and Function fields can betransferred within standard CAN Bus fields e.g.

-   -   Within the DATA fields by defining specific formats and        delimiting to allow identification of destination address,        function and associated data    -   Within and a replacement of the INDENTIFIER EXTENSION (18 bits)        to transfer Destination Address and Function information

Use of a bus such as a CAN Bus combined with a higher level destinationaddressing scheme, for example, can provide the following modes ofoperation.

A central electronic processor issues messages to a distributed sensingnode (input) to collect (or read) data—e.g. temperature data;

A central electronic processor issues messages to a distributed controlnode (output) to set an output condition—e.g. set a fan speed PWM signalto a condition that controls fan speed;

Allow a distributed control node (output) to receive a message (orquery) from a sensing node to control an output in response to theinput. E.g. adjust fan speed autonomously and directly in response to atemperature change;

And/or allow a distributed node to send an immediate message to theelectronic processor to notify an alarm condition without waiting for itto be first interrogated by the electronic processor.

That is, operation of input sensors and output components may beautonomous and/or under management of an electronic processor of adisplay.

Every node has the ability to detect any error in transmission e.g. as aresult of noise, in which case any node can raise an error flag whichdestroys the bus traffic, signalling for the message to be automaticallyresent without any associated software overhead. As an example,temperature data sourced from multiple locations can be acted uponautomatically by multiple devices e.g.

a) various active components e.g. fan controller able to adjust fanspeeds automatically to maintained a desired temperature;

b) electronic processor to change operating states e.g. between coldstart, warm start, power save, normal operating state, cold operation,hot operation etc;

c) electronic processor and/or other active components to adjust displaybrightness.

Input sensors may include a Front Facing pixel sensor to detect programon a display or a door sensor to detect if a door is open or closed.

Output components may include simple devices such as an LED indicator toshow an alarm state locally; or output ports or circuits that can beconfigured or set to a desired state e.g. ON/OFF, PWM, Analogue levele.g. voltage level, or other signal state or condition.

The microcontroller on-board each and varied intelligent input/outputmodule performs varied operational functions determined by itsself-addressing configuration programming e.g.

-   -   Detecting its “address” from local position inputs e.g. DIP        switch or cable wiring configuration    -   Self-configuring its operation and signal condition dependent on        the “address” that is chosen at the specific location; where        inputs may be wired to different sensors within the display e.g.        -   Front/rear LCD panel, top/bottom/centre of display panel,            electronic control assembly,        -   Processing signals in different ways e.g. process ambient            light instead of processing LCD Display Pixel light.        -   Process Mains power fail functionality rather than a PC            watchdog timer.    -   Detecting applied sensors e.g.        -   Tilt switches        -   Video signal e.g. for presences or loss of video signal        -   Temperature        -   Humidity        -   Input mains power        -   Battery voltage        -   Fan speeds        -   Ambient Light        -   Shock        -   Display Pixel Light (RGBc)        -   Energy usage e.g. meter        -   And potentially any input sensor applicable to the            application    -   Conditioning and processing of input signals/sensor inputs e.g.        -   De-bouncing “changes in state” of input sensors to record            steady state values        -   Applying default readings (e.g. maximum or minimum settings)            to sensors that are not connected or operating out of normal            operation to prevent spurious conditions occurring during            subsequent calculations e.g. “divide by zero”        -   Processing watch dog timers to ensure attached devices are            operational e.g. PC        -   Detecting changes in state of signals for potential alarm            notification purposes e.g. loss of power, loss of video            signal, door open, local or remote reboot signals, module            start-up/power up, where immediate action needs to be taken.    -   Processing of output signals for controlling actuators e.g.        -   Applying timers to the control of outputs such as            automatically turning off outputs after a configured period            e.g. turn off heater automatically after a configured period            until re-instructed by PC to prevent overheating if the PC            crashes.    -   Responding to POLLS from the MASTER (e.g. PC), through the        “destination addressing layer” within the CAN BUS protocol such        as        -   Communicating the requested “conditioned” sensor reading to            the PC e.g. temperature, or        -   Activating an output such as turning ON a heater, under            further conditioning control from the microcontroller e.g.            maximum ON period before automatically turning off    -   Generating NOTIFICATIONS to the MASTER e.g. PC

FIG. 9 illustrates elements and components for a Cold Start process in alarge-scale electronic display unit.

A hardened 12 V Power Supply Unit (PSU) 200 supplies power to a PowerManagement Board (PMB) 201 and optionally to a fan 208 for guidingcirculating air across humidity and temperature sensors. The PMB 201receives data from one or more temperature sensor 204 and humiditysensor 205, both of which are disposed in internal circulating air. Aprimary heat source 202 (e.g. mains powered, 600 W) provides rapidheating of internal circulating air and is controlled by the PMB 201.Connections between the PSU 200 and the PMB 201 and optional fan 208 aredirect, hardwired connections. Connections between the PMB 201 and thecomponents 202, 204, 205 are direct, hardwired connections. A furtherdirect, hardwired connection is made from the PMB 201 to 48V PSUs 318for fans 102 that cause flow of internal air through an associatedheat-exchanger.

The PMB 201 is also connected to a CAN bus that provides multiplexedcommunication for sensitive electronics such as a PC 206 and router 207;sensitive display electronics that may include 24V PSUs 319, videocontroller 316 and LCD panel 313; and further sensors and controlcircuits 323 (which may include an I/O controller).

It will be appreciated that voltage and power values that are given inthis description are by way of example only. Voltage and powers otherthan 24 v, 48 v, 600 w may be adopted. More than one heater or heatsource may be employed.

Operation of the elements and components illustrated in FIG. 9 isapparent from the preceding description and legends in the figure. Itmay be noted that mains powered components (12 v PSU 200, heater 202)are most at risk from condensation when power is first applied, andtherefore are desirably “hardened” e.g. through sealing or conformalcoating.

Lower voltage circuits (e.g. PMB 201, 12 v fan 208, sensors 204, 205 andpotentially the CAN bus circuits) do not necessarily need to be“hardened”, since Cold Start will usually occur infrequently andtherefore any condensation we'll have a low risk of impurities. Oncestarted, the display unit is temperature and humidity controlled topresent a low risk of further condensation.

Other circuits may become increasingly sensitive to environmentalconditions—e.g. PC/ROUTER 206, 207 and in particular the displayelectronics (e.g. LCD panel 313, video control 316).

FIG. 10 illustrates a Warm Start process for a large-scale electronicdisplay unit. The process may be understood by following the flowchartof FIG. 10.

Initially, Warm Start can be thought of as an extension to Cold Start(when the unit is first powered), where the PC takes further measures toensure that the environmental conditions are acceptable to turn on theLCD panel (which is the most environmentally sensitive component in thesystem, distributed over a wide area, closer to cooler, external glassand susceptible to wider environmental temperature variations).

However, Warm Start is also entered after completing the Powersave state(which turns off the LCD panel) in order to ensure (again) that theconditions are acceptable before turning the LCD Panel back on.

Although the Powersave state will maintain a minimum internaltemperature within internal circulating air, the metalwork willgenerally be at a lower temperature, since it is typically in thermalcommunication with external (ambient) cold air overnight during powersave times.

The heat-exchanger fans for external air will be off when entering theWarm Start process, as there would be a risk of condensation as a resultof starting the external heat-exchanger fans, which will lower internalair temperature and raise RH. Turning on the external heat-exchangerfans will have the effect of drastically dropping internal airtemperature when the external heat-exchanger fans are turned on if theambient air is cold.

There is a need to raise the heat of the unit as quickly as possible inorder to reduce humidity. The initial startup temperature can be madehigher than normal operational temperature to aid heating up of themetalwork by turning on the backlight as well as the heater.

Warm Start will therefore ensure that temperature on and around the LCDpanel is acceptable before turning on the LCD Panel. Once the LCD panelwith backlight is on, the internal temperature level will be set to HIGH(for an initial warm up period) and control passed to the NormalOperation process (detailed below), so that the Normal Operation processcan raise the internal operating temperature for a period of time whilstthe metalwork warms up and temperatures stabilise.

FIG. 11 is a schematic diagram of elements and components for use incontrolling dew point with a crossflow heat-exchanger 100 of alarge-scale electronic display unit. As seen in FIG. 11, external airflow through the heat-exchanger 100 is from right to left and internalair flow is from top to bottom.

Temperature and humidity sensors 300-311 are located in significantareas in order to manage internal temperature and to calculate dewpoints to manage humidity and condensation. Significant locations are:

-   -   304, 305—Ambient external air input at the hottest part of the        heat-exchanger 100 where the associated fan 101 delivers most        air flow and there is therefore the least risk of condensation.        Knowing ambient air temperatures provides guidance on risk of        condensation when compared to internal air temperatures.    -   308, 309—Located on metalwork of the heat-exchanger 100 in the        area of most condensation risk, where the output of the internal        airflow meets the input of the external airflow and where the        temperature differential is lowest.    -   300-303—Input and output sides of internal air flow through        heat-exchanger 100, where temperature differentials and dew        points can be calculated with reference to ambient air        temperatures.    -   310—Within internal circulating air paths near a controllable        heat source e.g. LED backlight 312 of LCD panel 313.    -   311—One or more temperature sensor within internal circulating        air flow between LCD panel 313 and solar load.    -   306-307—Output side of the external air flow from the        heat-exchanger 100, to enable determination of the level of heat        removed from the unit and association of temperature        differentials with external ambient air input, internal air        input and output to heat-exchanger 100, to help with the        calculation of dew points across the heat-exchanger. Temperature        and humidity sensors need not be provided at all of the above        points.

When the unit is cold, the external fans 101 are turned off, allowingthe heat source 202 (and optionally 312) to pre-heat the unit to raiseRH. In this case, as one alternative, the LED backlight could solely beused as the heat source without a separate, dedicated heater to raiseinternal temperature. Cold air is then brought into the heat-exchanger100 to cool the unit to operating temperature and dew points calculatedin the above significant areas to determine the risk of condensation.External fans are backed off if necessary, to ensure condensation cannotdevelop.

As the metalwork of the unit heats up, a closed loop temperaturecontroller can regulate temperature to desired operating levels bycontrolling the fans 101, 102 individually for efficient heat exchange,as discussed above.

Other elements and components of the display unit include 12V PSU 200,PMB 201, controllable heat source 202, dehumidifier 203, driver 314 forLED backlight 312, sensitive control electronics 315 (e.g. PC,peripherals, router), video control electronics (e.g. scaler, timingcontroller), fan 317 for control electronics 315, 48V PSU 318 for fanscontrolled by PMB 201, 24V PSU 319 for LCD panel 313 (controlled by PMB201), hydrophobic filter 320 (e.g. Gore vent) to aid air pressureequalisation between internal and external (ambient) air, controller 321for individual control of internal circulating air fans 102, andcontroller 322 for individual control of external heat-exchanger fans101.

FIG. 11 illustrates one example of a module 306A connected totemperature sensor 306 and provided with microcontroller 306B. Anothermodule is in the form of external fan controller 124, provided withmicrocontroller 124B. Internal fan controller 125 affords a similarmodule. In the interests of clarity, not all modules andmicrocontrollers are individually shown and referenced in FIG. 11. It ispossible for a given module to connect to more than one input sensorand/or output component—for example, both temperature sensor and an airfan.

Operation of the elements and components shown in FIG. 11 will beunderstood from the foregoing description, including the descriptionwith reference to FIGS. 1 to 6.

FIG. 12 is a diagrammatic view of a heat-exchanger 100 to illustrateareas at risk of generating internal condensation. The view is similarto that of FIG. 4, the heat-exchanger 100 having horizontal channels(103) for external air and vertical channels (104) for internal air.

Top right corner 351 is the location of the heat-exchanger 100 wherethere is the biggest differential between internal and external airtemperatures, and where there is therefore least risk of dew pointcondensation.

Bottom right corner 352 is the location where RH is likely to be higherin the local area around the metalwork—i.e. where coldest external air(conducted through to internal side) meets least differential betweeninternal and external air temperatures. If this cools the air around themetalwork to dew point, then this will result in condensation.

Arrows 353 show increasing external air temperature (from bottom rightto top left). Although temperature differential is substantiallymaintained, it does so at a higher base external air temperature, whichis at less risk of condensation as RH is lower.

Arrows 354 show decreasing internal air temperature (from top right tobottom left). Although temperature differential becomes low, it is at ahigher base external air temperature, which is at less risk ofcondensation as RH is lower.

Fans 101 and 102 are controlled individually. 351 is the location of theexternal fan 101 to be turned on first, where there is the biggestdifferential between internal and external air temperatures, and wherethere is least risk of dew point condensation. The external fan 101 atlocation 351 is also the last to be turned off.

The external fans 101 below that at location 351 are sequenced on inturn (top to bottom) at minimum speed, as risk of dew point condensationreduces. They are turned off in reverse order as cooling is reduced.

Fans 101 and 102 are preferably controlled individually, although allfans 101 could be controlled together and all fans 102 could becontrolled together.

The speeds of fans 101 and 102 may be controlled to achieve efficientoperation of the heat-exchanger 100, along the lines discussed abovewith reference to FIG. 6, for example.

FIG. 13 is a flowchart illustrating a Normal Operation process of alarge-scale electronic display unit. The process may be understood byfollowing the flowchart of FIG. 13.

During Warm Up, the internal operating temperature will be kept highinitially, as cold air is brought into the heat-exchanger of the unit.As temperatures stabilise to provide sufficient cooling for the desiredbacklight brightness level (e.g. metalwork warmed up), then the internaloperating temperature will be reduced to a normal operating temperature

The initial startup temperature will drop quickly when cold air isinitially brought in through the external fans. The external fans mustbe stopped (initially) or reduced as the units heat up, if dew pointmeasurements/calculations show risk of dew point condensation.

The external fan in the hottest area of the heat-exchanger is turned onfirst (e.g. top right in FIG. 12) where there is the biggest temperaturedifferential (that minimises risk of condensation). The heat-exchangerexternal fans are then sequenced on in turn (top to bottom at minimumspeed)

If the temperature is too excessive and cannot be cooled without risk ofcondensation, then the level of the heat source (e.g. backlightbrightness) must be reduced until an acceptable operational temperaturecan be reached.

As the unit begins to cool (e.g. at night) then the externalheat-exchanger fan speeds will be reduced, in a ratio that allows theheat-exchanger to operate efficiently. The external air fans will turnoff in turn in reverse order (to turning on)—i.e. coolest fans first.

The control element of temperature management ensures that the externalheat-exchanger fans are reduced or turned off where temperature/humiditymeasurements (or calculations) show risk of condensation developing inthe heat-exchanger.

If the backlight cannot generate a sufficiently high temperature whenambient conditions get too cold, then the dedicated heater is turned onto raise the temperature. This heater may be used to manage temperaturebetween high and normal temperature conditions to provide hysteresis inmaintaining temperature in these conditions without causing condensationissues.

Normal Operation (warming up)—The Warm Up phase can be exited whentemperatures stabilise without drastic change as a result of turning onthe external heat-exchanger fans; whereby the heat-exchanger fans are onat the desired levels without risk of condensation. It is worth notingthat environmental conditions may be so cold that a normal operatingtemperature can be maintained without overheating, with the externalheat-exchanger fans off—e.g. the metalwork cools the unit without theneed to take in cold external air.

Normal Operation (nominal)—Under normal operating conditions, theinternal operating temperature is managed to an acceptable temperatureband as part of a closed loop system that adjusts the level of coolingbased on the heat generated in the unit—e.g. due to brightness of thebacklight and/or solar load. The higher the brightness of the backlight,the higher the cooling as a result of operating the heat-exchangerinternal and external fans faster; and that tends to optimiseheat-exchanger efficiency. The outdoor display will generally getincreasingly warmer as the day continues e.g. as the sun reaches maximumtemperatures. The temperature management system will adjust externalheat-exchanger fans (and internal fans) accordingly to maintain adesired operating temperature

Normal operation (Hot)—if insufficient cooling can be achieved tooperate the electronics of the unit within specification then, forexample, the backlight brightness is gradually reduced. Under worst caseconditions, all heat sources are turned off until satisfactory nominaloperating conditions arise. If temperature is excessively high thenthere is no/very little risk of condensation.

Normal Operation (Cooling)—As the environment gets colder, e.g. at duskor night time, the heat-exchanger fans are successively reduced in speedat an appropriate ratio (for an efficient heat-exchanger operation).Then external air fans are successively turned off (from bottom to top)such that the fans most at risk of causing condensation (leastdifferential) are turned off first. As the units get cooler, provisionis made to retain heat over the cooler period (before all external fansturned off) by operating at a higher internal temperature (e.g. similarto warming up) by reducing the external air flow further, to keep RH aslow as possible when the external fans are finally fully turned off.This may keep the unit as warm as possible before entering Powersavemode, which will reduce the need to turn the heater back on inPowersave. If there is insufficient heat to lower RH for the desiredbacklight brightness (or temperature falls too low), then the unit willturn on the dedicated heater to increase heat and reduce RH to desiredlevels—particularly since it is not desirable to raise backlightbrightness to generate heat when ambient light levels are low.Furthermore, local regulations may set a maximum light level thatoutdoor screens can operate at between dusk and dawn in order tominimise light pollution. In this case the dedicated heater may beturned on or off to manage temperatures in these conditions between highand normal levels.

FIG. 14 is a flowchart illustrating a Powersave process of a large-scaleelectronic display unit. The process may be understood by following theflowchart of FIG. 14.

Powersave mode is typically entered at a desired time of day setting(e.g. 2.00 am), when normal operation is not required e.g. outsideadvertising times. It is desirable to maintain a minimum temperatureband within the unit to ensure sensitive electronics maintain operation;and where there is no risk of condensation by temperature/humidityreaching dew points on internal surfaces.

Under risk conditions, the dedicated heater is turned on to increasetemperature, reduce RH and raise the dew point. If the heater is notable to generate enough heat over a period of time, then the backlightcan be turned on and the brightness gradually increased untiltemperature, RH & dew points are at acceptable levels. As analternative, the LED backlight can be used alone to raise temperaturewithout use of a dedicated heater; where the LCD panel is turned off sothat content is not displayed.

Once safe levels have been reached then the heat source (backlight andheater) can be reduced/turned off and the process repeated until timesettings (or when instructed) exit from the Powersave mode. The unitmust then go into Warm Start mode in readiness for full operation.

Hysteris is therefore required to permit the heating and cooling tooccur over an acceptable band in order to manage temperature and RH toacceptable levels. Internal temperature remains above minimum conditionsso that condensation does not cause long term issues with low voltagenon-hardened electronics.

Powersave may be exited early in the morning when external temperaturesare cold. Cold external air is in thermal communication with theinternal metalwork. Therefore, although internal air temperature maybecome warm, metalwork will likely be at a much lower temperature. Caretherefore has to be taken before entering Normal Operation mode toensure that cold air brought into the unit does not cause internalcondensation—hence the need to exit to the Warm Start mode first.

The term PC is used frequently in the art of digital displays and isused conveniently in this specification to denote any suitable dataprocessor. More than one PC may be provided, each for controllingdifferent functions within the display.

It may be noted that humidity measurements may be accurate only wherethe temperature is above 0° C., as frozen water (solid) returns to aliquid state. Likewise, dehumidifier operation can only take place above0° C. when frozen water (solid) has returned to a liquid state. Wheretemperature is at or below 0° C. then humidity is assumed to be 100%e.g. for the purpose of calculating Dew Point Temperature.

Humidity sensors typically have a built-in temperature sensor, sowhenever a humidity reading is taken (relative or otherwise), it may betaken relative to the temperature in the same location. Thus, allhumidity readings from sensors may be recorded at the same time andlocation as associated temperature readings from the sensors, in orderto determine the humidity relative to temperature (i.e. “RelativeHumidity”) for the purpose of calculating dew point.

Whilst LCD display panels, typically with LED backlights, are disclosedin this specification, electronic display panels of other types mayalternatively be employed, where practical—for example, LED or plasmadisplay panels—or oLED display panels (which do not necessarily requirea backlight). Where an electronic display panel requires a backlight,the term ‘display panel’ is to be understood to include such abacklight, unless the context requires otherwise.

In this specification, the verb “comprise” has its normal dictionarymeaning, to denote non-exclusive inclusion. That is, use of the word“comprise” (or any of its derivatives) to include one feature or more,does not exclude the possibility of also including further features. Theword “preferable” (or any of its derivatives) indicates one feature ormore that is preferred but not essential.

All or any of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), and/or all or any ofthe steps of any method or process so disclosed, may be combined in anycombination, except combinations where at least some of such featuresand/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings), may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. An electronic display comprising: a housingthat is divided internally into regions; a display panel within one ofsaid regions and having a display surface that is visible through thehousing; and a cooling module disposed within the housing and arrangedto provide a flow of gaseous internal coolant through the cooling moduleand said regions, the cooling module having a crossflow heat-exchangerwithin the cooling module and side walls that define a path of flow ofthe internal coolant through the cooling module; wherein each of saidregions and said cooling module has a respective internal coolant inletand internal coolant outlet; wherein the internal coolant inlets of saidregions communicate with the internal coolant outlet of the coolingmodule and the internal coolant outlets of said regions communicate withthe internal coolant inlet of the cooling module; the arrangement issuch that, in use, each of said regions has its own circulating loop ofinternal coolant, through the respective said region and the coolingmodule, with flow of internal coolant being deflected by a deflectingsurface from the outlet of the cooling module towards the internalcoolant inlets of said regions, and flow of internal coolant from theinternal coolant outlets of said regions being deflected by a deflectingsurface towards the internal coolant inlet of the cooling module; andthe internal coolant flows in parallel, in the same direction, over andcools both front and back of the display panel, the display panel beingspaced from the side walls of the cooling module.
 2. The electronicdisplay according to claim 1, comprising a plurality of display panels,each arranged as aforesaid in a respective one of said regions.
 3. Theelectronic display according to claim 1, wherein one of said regionsdoes not have a display panel within it.
 4. The electronic displayaccording to claim 1, wherein said regions comprise a front region and aback region of the housing; and the display panel is disposed in thefront region with the display surface visible through a front face ofthe housing.
 5. The electronic display according to claim 1, wherein thecooling module side walls extend between side walls of the housing. 6.The electronic display according to claim 5, wherein the side walls ofthe cooling module divide the housing into said regions.
 7. Theelectronic display according claim 1, wherein the internal coolant inletand internal coolant outlet of the cooling module face and are spacedfrom side walls of the housing.
 8. The electronic display according toclaim 1, wherein one of said deflecting surfaces is provided by aninternal coolant deflector that faces the internal coolant outlet of thecooling module and is operative to deflect internal coolant from thecooling module into different circulating loops of internal coolant indifferent said regions.
 9. The electronic display according claim 1,wherein one of said deflecting surfaces is provided by an internalcoolant deflector that faces the internal coolant inlet of the coolingmodule and is operative to deflect internal coolant from differentcirculating loops of internal coolant into the cooling module.
 10. Theelectronic display according to claim 1, wherein said cooling modulecomprises an impeller for providing a flow of internal coolant throughthe cooling module and said regions.
 11. The electronic displayaccording to claim 10, wherein said crossflow heat-exchanger has a pathfor external coolant that is introduced into the crossflowheat-exchanger from externally of the housing and output from thecrossflow heat-exchanger to externally of the housing, the externalcoolant exchanging heat with internal coolant within the crossflowheat-exchanger without direct contact between the external and internalcoolant.
 12. The electronic display according to claim 11, wherein saidexternal coolant is air.
 13. The electronic display according to claim10, further comprising an electronic control assembly arranged tocontrol functions of the electronic display, the assembly being locatedin said cooling module downstream of the crossflow heat-exchanger sothat cooled internal coolant from the crossflow heat-exchanger passesover the assembly.
 14. The electronic display according to claim 13,wherein said electronic control assembly comprises components within anenclosure having an inlet and outlet for internal coolant and at leastone impeller arranged to provide flow of internal coolant through saidenclosure.
 15. The electronic display according to claim 1, wherein saidinternal coolant is air.
 16. The electronic display according to claim1, being a large-scale electronic display.
 17. The electronic displayaccording to claim 1, wherein said display panel is an LCD panel. 18.The electronic display according to claim 1, wherein said display panelhas an associated backlight.
 19. The electronic display according toclaim 1 and further comprising: an electronic processor arranged tocontrol operating conditions within the housing; input sensors disposedwithin the housing at distributed locations and arranged to senseoperating conditions within the housing; output components disposedwithin the housing at distributed locations and arranged to respond tocontrol signals; and a bus connecting said input sensors, outputcomponents and electronic processor for intercommunication: whereinprocessing of signals received from said input sensors and controlsignals passed to the output components is distributed amongstmicrocontrollers that are local to said input sensors and outputcomponents and connect said input sensors and output components to saidbus.
 20. The electronic display according to claim 19, wherein saidoperating conditions comprise environmental conditions.
 21. Theelectronic display according to claim 20, wherein said input sensorscomprise humidity sensors and temperature sensors.
 22. The electronicdisplay according to claim 19, wherein said output components areoperative to adjust environmental conditions.